Physiology 206 Lecture 16 Outline of Last Lecture I Collateral vessels II Shock III Heart attack IV Infarction V Brain circulation VI Respiration Outline of Current Lecture I Thoracic cavity II Diaphragm III Intercostal muscles IV Bronchioles V Obstructive disorders VI Elasticity of lungs Current Lecture 2 21 14 1 ATM 760mmHg Pressure N volume When air moves moving down pressure gradients o Alternatively reducing and increasing pressure in alveoli o Inspiration inhaling below atmospheric pressure o Expiration exhaling above atmospheric pressure Thoracic cavity o If pressure decreases pulls on lungs expanding them inhalation o If pressure increases lungs can t expand exhalation collapses lungs o Pressure in thorax is below atmospheric pressure Keeps lungs from collapsing Our natural tendency is to relax These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Prevent collapse by keeping an air tight box which is the thorax Diaphragm dome shaped muscle at the bottom of the thoracic cavity o Innervated by phrenic nerve Intercostal muscles around the ribs o External intercostal muscles outside of ribs Pulls ribs up and away from the spinal column when the muscle contracts Increases the volume in the thorax Expiration is passive When exercising o Contract the external intercostals more o Contract internal intercostals Pulls ribs inward Forced exhalation Contract abdominal muscles o Push in abdomen o Push diaphragm up o Reduce thoracic volume Poiseville s Law o Resistance to flow laws Bronchioles account for most of resistance in air flow o Smooth muscles in walls o Can change diameter Change airway resistance o Parasympathetic stimulation bronchioles restrict o Sympathetic stimulation bronchioles relax Ex asthma Spastic contractions of bronchial smooth muscle Increasing restriction of air flow Must use muscles to exhale o Obstructive disorder Airway resistance increases o Other pulmonary disorders Restrictive disorders Resistance remains the same volume reduced Ex pneumonia o Fluid leaks into the alveoli Elasticity of lungs o Elastic fibers resist being stretched o LaPlace s Law Pressure surface area inside the sphere increases as the diameter decreases
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